Joining workpieces with similar or dissimilar material properties has become increasingly important as industries strive for reduced weight and improved performance from engineering structures such as automotive, aeronautical, and nautical, among others. Staking has the capacity to join dissimilar plastics to one another or join plastics to other materials (e.g., metal). Staking has the advantage over other mechanical joining methods in eliminating the need for additional components such as rivets and screws.
Traditional staking connects workpieces by creating an interference with a first workpiece including a hole and a second workpiece including a stud that inserts into the hole of the first workpiece. A staking punch is then used to compress the stud axially, which reforms material within the stud into a stake that permanently joins the workpieces without the use of additional components such as screws and rivets.
Similar to traditional staking, heat staking begins with a plastic stud on a second workpiece being inserted into a hole located within the first workpiece. However, in heat staking, material within the plastic stud is reformed using controlled heating and melting to produce a stake which mechanically locks the workpieces together without the use of additional components such as screws and rivets.
Reformation of the plastic stud is traditionally achieved by heating material of the plastic stud, using super-heated air or a thermode, above a glass-transition temperature associated with the material, creating a softened material. Pressure is then applied to the softened material in order to create the stake.
Using super-heated air to heat the material of the plastic stud requires the use of hot air jets, which often over time lead costly maintenance of components such as individual flow meters associated with the hot air jets. Also, using a thermode to heat the material of the plastic stud can require additional processing time for each stake because the thermode is heated and cooled down for each connection. Additionally, hot air jets and use of multiple thermodes for multiple connections can require lengthy tooling changeover times.